I see coloured pellets. What have they been eating? Spread some fresh poop with your finger on white paper to make sure it's not just darker than normal. If it is black then take the budgie to an avian vet.
Black poop means they have eaten something like blackberries, or there are dark colored pellets in their food or they have upper gastric system bleeding going on. If it is the latter they should have gone to the vet two days ago.
If your budgie has been acting ill then they should be seen by a vet. The colour of the poop if it is a change from normal without a diet change can be a sign of illness. I'm assuming this is not the usual colour?